Referring to FIG. 1, the typically partitioned hard disk includes three main parts 10, 20 and 30. A first part 10 is dedicated to a master boot record (MBR). The master boot record is a small piece of code that is executed when a computer boots up. Typically, the MBR resides on the first sector of the hard disk of a computer. The MBR can also reside on removable media such as a floppy disk or CDROM which may be used to boot the computer. The MBR contains a partition table that is used to determine which partition to use for booting. The boot process transfers program control to the boot sector of that partition, which continues the boot process. Thus, the MBR includes a table of addresses and a set of instructions for loading a boot sector of an operating system.
A partition divides memory into isolated sections. In DOS systems, a disk can be partitioned, and each partition behaves like a separate disk drive. Partitioning is particularly useful if it is intended to run more than one operating system on a machine. For example, one partition might be reserved for Windows and another for UNIX.
A second part 20 of a legacy-partitioned hard disk is known as the end of track. This is unused except by some setup programs in WINDOWS OS. The reason for the end of track 20 is that the legacy partitioning scheme requires a partition to start on a track boundary, and the MBR 10 does not occupy the entire track. The end of track 20 occupies the remainder of the first track not occupied by the MBR 10.
End-of track 20 forms a forbidden part in the sense that it is not listed in the table of addresses of the master boot record. A third part 30 stores an operating system, and in particular a boot sector of the operating system, which is listed in the table of addresses of the master boot record. The third part 30 includes a main active partition and up to three other partitions, whereby these ‘extended partitions’ may be further sub-partitioned.
It is known to use the forbidden part for locating some maintenance tools and also, to store a Globally Unique Identifier Extensible Firmware Interface GUID Partition Table (GUID-EFI-GPT), developed by INTEL, for locating a second table of addresses.
According to this boot scheme, firmware accesses the second table without reading the instructions contained in the master boot record.
When operating a computer, it is often necessary to use a supplementary operating system, particularly for maintenance tasks. For example it can be necessary to activate a lower level operating system such as DOS for reflashing the BIOS of a computer. A second operating system may be loaded by means of a command interpreter contained on removable media such as a floppy disk or a CDROM.
It has also been proposed to store a second operating system, in the partition corresponding to the main operating system, in the form of a series of files relating to the first operating system (OS). Those files are stored as other files in the partition of the first operating system.
However, such systems do not generally provide the full functionality of a supplementary operating system. Moreover, in such a situation, it is necessary to load or activate the first operating system in order to load the second one. Furthermore such systems can sometimes be unreliable in terms of hardware and software conflicts.
It is also known to provide software tools which can change the partition configuration of an initially single-OS-disk. These can be used to reduce the size of the partition dedicated to the main operating system, and create a fourth partition in the space initially contained in the third partition. The fourth partition may then be loaded with the second operating system. However such software tools can be complex and expensive. Further, they can be difficult to use and, given the relatively low-level at which their operation is generally carried out, the consequences of a mistake can render a disk unusable.